501 Not Implemented

The HyperText Transfer Protocol (HTTP) 501 Not Implemented server error response code indicates that the server does not support the functionality required to fulfill the request. This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource. The only request methods that servers are required to support (and therefore that must not return this code) are GET and HEAD.

Notes:

A 501 error is not something you can fix, but requires a fix by the web server you are trying to access.